Double metal cyanide complexes are well-known catalysts for epoxide polymerization. These active catalysts give polyether polyols that have low unsaturation compared with similar polyols made using basic (KOH) catalysis. The catalysts can be used to make many polymer products, including polyether, polyester, and polyetherester polyols. The polyols can be used in polyurethane coatings, elastomers, sealants, foams, and adhesives.
DMC catalysts are usually made by reacting aqueous solutions of metal salts and metal cyanide salts to form a precipitate of the DMC compound. A low molecular weight complexing agent, typically an ether or an alcohol is included in the catalyst preparation. The complexing agent is needed for favorable catalyst activity. Preparation of typical DMC catalysts is described, for example, in U.S. Pat. Nos. 3,427,256, 3,829,505, and 5,158,922.
We recently described highly active DMC catalysts that include, in addition to a low molecular weight organic complexing agent, from about 5 to about 80 wt. % of a polyether having a molecular weight greater than about 500 (see U.S. Pat. No. 5,482,908). Excellent results are obtained when the polyether component of the DMC catalyst is a polyoxypropylene polyol. Compared with earlier DMC catalysts, the polyether-containing DMC catalysts have excellent activity and give polyether polyols with very low unsaturation. In addition, polyether-containing DMC catalysts such as those described in the `908` patent are easier to remove from the polyol products following epoxide polymerization.
The polyether-containing DMC catalysts that we described earlier are valuable because they give polyether polyols with low unsaturation, and they are active enough to allow their use at very low concentrations, often low enough to overcome any need to remove the catalyst from the polyol. Catalysts with even higher activity are desirable because reduced catalyst levels could be used.
One drawback of polyether-containing DMC catalysts now known (and DMC catalysts generally) is that polyol unsaturations increase with epoxide polymerization temperature. Thus, polyols prepared at higher reaction temperatures (usually to achieve higher reaction rates) tend to have increased unsaturation levels. This sensitivity of unsaturation to increases in epoxide polymerization temperature is preferably minimized or eliminated.
An ideal catalyst would give polyether polyols with low unsaturation and would be active enough to use at very low concentrations, preferably at concentrations low enough to overcome any need to remove the catalyst from the polyol. Particularly valuable would be a catalyst that can produce polyether polyols having very low unsaturation levels over a broad range of epoxide polymerization temperatures.